Created attachment 438871[details]
gnome-power-manager-2.31.6-backlight-is-None.patch
The problem (at least for my machine) is that some part of the system (upower? kernel? who knows) doesn't know how to deal with the backlight brightness. So gpm_backlight_init does:
backlight->priv->brightness = gpm_brightness_new ();
which sets backlight->priv->brightness to 0 (i.e. None). So when we get to gpm_backlight_brightness_evaluate_and_set(), we end up trying to read the X property for something that's None, and X barfs at us, and gpm crashes.
Okay. So. Adding a nice simple check to gpm_brightness_output_get_internal():
if (brightness->priv->backlight == None)
return FALSE;
lets gpm at least start up and run without crashing. Brightness control obviously isn't working, and it doesn't think I have a lid on my laptop, but at least we're not crashing.